This invention relates to a closure for a thermoplastic bag and more specifically, this invention relates to an adhesive closure arrangement for a flexible thermoplastic bag.
Adhesive type closure arrangements have been used to seal and/or close plastic bags such as those used for sandwiches, garbage containers, and other household uses. For example, U.S. Pat. No. 4,519,095 describes an adhesive channel closure suitable for use with flexible bags, such as thermoplastic bags, especially those made from polyethylene, wherein the closure comprises at least one female channel member or strip-affixed to the bag and having a pressure sensitive adhesive layer on an internal portion of the channel strip such that the thickness of the adhesive layer is less than the interior depth of the walls of the channel strip. During shipment and storage the walls of the channel hold the pressure sensitive adhesive layer away from adjacent surfaces to prevent inadvertent sticking. Sealing of the bag is achieved by contacting the channel strip with a surface of the bag and exerting pressure along the strip whereby the pressure sensitive adhesive is contacted with a substantially flat portion of the surface and adhered thereto.
U.S. Pat. No. 4,519,095 shows a channel with the adhesive layer positioned on a flap of the bag; a channel with the adhesive positioned on the body of the bag over which the flap will fold; and two female channel strips positioned on opposite sides of a bag opening to affect a double seal by pressing the two channels into contact such that one wall or bead of each channel is contacted by the adhesive layer in the opposing channel.
One problem with the adhesive closures having rigid channel strip ribs described in U.S. Pat. No. 4,519,095 is that the closures are not easy to close. A sufficient amount of pressure applied to the rigid channel strip ribs is required to overcome the rigidity of the ribs to effectuate a closure. In addition, the closure requires restricting the width between the ribs to a predetermined width in order to avoid premature contact of the pressure sensitive adhesive with the opposite contact surface wall during processing and shipping of the bag, i.e., to avoid premature closure. The channels are also too small to accommodate the thumb of a user. Also, there is less surface contact between wall and adhesive because of the height and width of the channel. In addition, the bag surface adjacent the adhesive wrinkles easy causing an inadequate closure and leakage of liquids through the closure. Furthermore, there is no tactility indication on the closure described in U.S. Pat. No. 4,519,095.
Another problem with the closure described in U.S. Pat. No. 4,519,095 is that the external opening force is the same as the internal opening force of the closure. Thus, the contents of the bag will tend to fall out of the bag since the closure is easily opened from the inside and the closure does not have sufficient closure force to hold the contents in the bag when the bag is placed upside down or horizontally where pressure is exerted against the closure by the contents. On the other hand, if the adhesive is made strong enough to hold the contents, then the bag will be difficult to open.
It is desired to avoid the problems with the prior art closures and provide closures suitable for use with plastic bags wherein the closures are able to effect a satisfactory seal as needed.
It is also desired to provide a flexible bag with an easy external openable and resealable closure and yet have a stronger internal sealing force to prevent the opening of the bag from the inside due to the pressure of the contents when the bag is undesirably placed in a non-upright position.